Ofc get third summon

Assuming you havent gotten slug yet and your snake is fully leveled then it might actually cost you chakra in the long run, were you to recruit the summon just to then not even feed it. That's because the summon is recruited being fed. At that point you wouldn't be leveling the slug either and the attributes it would try to give are basically nothing anyways.

Having said that, I'd recruit the slug. Now, you might actually lose a very little bit of power in the short term with this plan... but it wouldn't take very long to eventually even get more power out of 2 active summons by recruiting slug and then starving your fully leveled snake instead.

A starved summon still grants 40% of its attribute bonus to the group. With around 220k, I think a starved snake versus a full-fed max-leveled snake is a difference of about 600 bp - not much, really - but not nothing either.

So... I would suggest you recruit your slug and start feeding it so that it can get you better bonus from being leveled - might as well start leveling it now because it takes quite awhile for a summon to level up to max and it sounds like you guys are behind the curve already.

Basically, feeding all 3 summons is a lot to ask for most groups... but you still want all of them max-leveled, even if you're not planning on feeding all of them.