Picked up the Poco M6 Pro 10 days back, and i think its safe to say that its probably the best phone under 15k, barring a few key parts. I got the 6/128 version, and coming from a similarly specced Samsung, its a breeze to use. I would highly recommend staying away from budget Samsung smartphones (apart from a few decent ones like F14, it comes with a slim version of OneUI), full OneUI is extremely taxing on budget phones. You'll notice lots of frame skips and animation jitters a few months after usage. MIUI/HyperOs on the other hand, is extremely well optimized, at the cost of bloat (which I'll get to in a bit).
Display is 90hz but its not very bright. Its good enough for indoor usage, but outside, you will have to squint sometimes to look at it. This is coming from a devout "low brightness" guy. Its size is an issue as well, you'll need to have wrists of steel to use it one hand, but you should get used to it after a while.
Battery life is excellent, I get around 10-11hrs of SOT (indoors + WiFi) with movies, browsing and a bit of PS2 emulation (RE4). Didnt check much outdoors, but I think it should be around 7-8hrs of SOT.
Cameras are surprisingly good, especially with a gcam port. I took a few pics, and found it on par or even better compared to OP Nord 2T and Samsung A8 (2018 model, it used to be a good flagship phone). Low light and selfies suck tho. Video stabilization is non existent as well (understandable for the price).
As for the bloat situation, yes its a nightmare. But I've got rid of 95% of it after spending an hour debloating it, and after that, HyperOS isn't even quarter as bad as people complain it to be. Lmk in the DMs if you need any help with it, it feels quite fresh to use after being bound to OneUI (I do miss GoodLock tho). If it helps, its update cycle is good as well, im on the June security patch.
Another key "feature" is its good custom rom support, albeit on TG. I bought it mainly to dabble in rooting and whatnot. I know it doesnt make much sense anymore but for a budget smartphone which didnt receive much love from Xiaomi, I think its fine.
You could consider the Samsung M34 as well, it has a slightly better SoC then M15, and after debloating it thoroughly, it should be good enough.