I was in the same boat as you didn’t want to spend over 1500 but wanted gmr15 reliability. I built mine with a aero epc upper and lower and the fit is amazing! I went with a Brekke customs 6” brake and buffer kit with smoke composite carbon buffer tube and smoke composite handguard. I waited for the best price on opticsplanet and found a Jp bolt and 10.5 barrel for feeding reliability. Got a Rise Armament pcc trigger, aero ambi charging handle, and radian ambi safety since I’m a lefty also from optics. Then finally Bcm stock with modified a2 grip that I had laying around to complete the build. I could not be happier just under 1500 all in all and unbelievable reliability, not a single malfunction with reloads or factory ammo. I have shot it and compared it next to a jp5, mpx, and tr9. Jp and mpx are definitely softer shooting and the quality of the jp5 is amazing! The tr9 is a beautiful gun but the lower and upper has some slop and is not as tight fitting as my gun and also feel mine balances better and is a softer shooter for 1/2 the price!
So you definitely can build a great quality gun for 1500 and get gmr15 reliability just have to do some searching for sales on quality parts.
