Evolve 65% A15 Machop?

What do you need a shitty IV Machamp for when you already have 3 high level ones?

I would. I evolve high level Pokemon with useful evolutions if they have 14/15 attack, regardless of their other IVs. Just standby your TMs.
I evolved a level 29 Gastly with 14 attack and 73% IVs.

Sure. I have two 75% IV C/DP Machamp that I uwe die gym sweeping. That 25% in difference is not gonna make any difference. It's not perfect if you're a collector, but it'll do the job in fights.

I personally would only invest in a high iv one. Although I see the logic behind evolving a high level one, I wouldn't invest any stardust into it however

Machamps are less important currently due to few people even doing Tyranitar raids (and even less Lapras, Snorlax).

It was critical to have Machamp immediately after Gen 2 hit due to Blissey walls and slow "quick" attacks (anyone remember that?)...and I still wanted my gym coins and dust.

I evolved a 80% Lvl 25 Machamp immediately to deal with the walls, but currently, with your 300k dust and poor IVs in general AND, you having 3 more, I'd just wait...175 isn't that much candies neither (I think I had over 500+ after a nest close by).

Just keep stocking up since you don't really NEED Machamp now (and you have 3 already).