That depends on the person.
For a fresh 32k, for example, it is a huge amount lost, since some of it will be their first gold in the slot, which will significantly impact their progression compared to their peers, causing additional loss due to competitive disadvantage thereafter.

For someone who have farmed 32k+ since 2.0 came out, except a very few that might be valuable for reforge effort, most of it is worth less than a silver exp pig, which is much cheaper (Granted, I have NO idea how much they sell silver exp pig for, but it'd be 13 of those). At the same time, the impact on progression is very minor (like 2-3 lv of tool lv only, or 3 reforges), which means they do not suffer additional losses from it. And 1500 coupon, which is flexible, spent elsewhere, might easily give more power than those minor upgrades.

Such is the law of diminishing return, the more you have of something, the less useful (and technically valuable) they becomes.

It's true that 3 reforges can potentially give up to 450 or so power (verfied by removing/adjusting magatama from ALL my ninjas)
But that' very unlikely.
To get 450, you would have to reforge 3 80 atk/nin into 3 empty slots. This is unlikely for the following reasons:
80 atk/nin is very rare, as it is only possible on red gourd. I've been farming 43200 for over a month now and I only have one 80. I do have 3 70s and 5 with >60 thou. Realistically, you'd get one 70s reforge and 2 60s reforge. This would drag the maximal reforge power value down to around 350.
The brothers TI drops are pretty high quality, and roughly half of them have full stat, which means you start with some good base tools. Now, if you are just starting reforge, you might still have empty slots, but that won't last for long. If you are replacing a stat as opposed to adding one, power gain will be halved at best.
We are talking about atk/nin stat, which you probably value over others when you did your initial stat selection. So it's even less likely for you to find an empty slot on a toll that doesn't already have atk/nin. Thus much more likely to halve the power gain. Considering that atk/nin stat are in fact the priority stat, if you are reforging any other stat, then chances are you are mostly done with atk/nin, which means you are likely to have fewer empty slot to reforge into.

Realistically, 3 reforge from a week of new tool will give you around 150 to 350 power, depending on where you are at on the "reforge progression".

In any case, I just did a 233 key pull on cave (200 plus rebate), that gained me about 450 power. Now, 1500 coupon isn't quite enough for that, but would cover over 2/3 the cost*, which means 300 power for 1500. And this is not counting the other stuff I got like purify stuff. Now, your cave might be higher than mine, thus diminishing return hits and you wont get quite as much power investing in there, but this is just ONE example, there are other ways to spend coupon, one of which might have higher yield (lucky board perhaps, that have a high % value yield in term of coupon cost, thou you only have limited control on rewards there)

Given that, 1500 coupon would be a reasonable amount of compensation for a veteran of the game, for the TI part. There is also the problem with missing roughly 12 medium thread. While there are ways to get it cheaper(lucky board), fact is that it have a face value of around 450 coupon. And if we take that out of the 1500, then the remaining 1050 will probably be insufficient. The cloth the gave is a joke and have no value for many players. So no, the compensation isn't enough, except for uber ptw who no longer need medium thread in which case the 1500 goes fully toward tools bit. But for some players, it is CLOSE to fair.

So let's not pull numbers out of your more private sections, but instead apply actual testing and logic, ok?

In any case, the root of the problem, and the original intend of my post, is that it would be rather difficult to properly compensate, as a fixed amount of compensation will be rather difficult to cover for different amount of loss, and in some cases, further losses as a result of that loss.

Personally, I think the best compensation would be 2 of the best tier of gold tools (paper shuriken, totsuka blade etc), 2 red gourd and 3 random gold tools.
For player who lost relatively little and no additional loss, this is just what it is, roughly 1 week of TI income.
For players who lost MORE than what they initially did due to missing a lot of power compared to their peers and thus suffer further losses as a result, this is likely MORE than what they lost(at first). As someone mentioned somewhere, it takes multiple weeks to get a full set of gold, and to have the highest tier ones, probably run into month territory. So this should give them more power than one week of TI normally would.

Probably the easiest and most fitting compensation to take care of the problem in difference in value. The alternative might require them bracketing different compensation according to power tier of the player, and then that gets into the subjective judgement of just how much additional loss does player suffer when they are at a certain power, and that might differ depending on the server (a 32k who is the only 25k+ in a server probably didn't suffer any additional loss, as he'd still win whatever, but a 32k in a server with lots of 30-34k would, in fact, lose a lot).
Thou this does carry the problem of giving gold tools to those who would have no access to them otherwise, meaning the sub-32k crowd. I'm not entirely sure what their extend of loss is. On the one hand, they are at low lv tools, probably, which means one week of tool exp would boost quite a bit. On the other, their tool are relatively low quality and are usually switched slowly and not in large batch(like at 32k mark), so that's complicated.

*2/3: this is if you buy key at cost of 50 for 560, there are BETTER deals out there, for example, the recent mystery fruit, which offers 88 for 799 (and you get extra rune to boot), this would make it 5/6 of the cost.