Brand new G4 (H815L) performance issues

Hey fellas!

Just got a new G4 to replace my Nexus 5, and I'm encountering some heavily disappointing performance issues like:

poor 3D performance - games like Boom Beach and Smash Hit run just... bad. mediocre/low fps gaming, where my Nexus 5 did perfectly fine!

2D performance (UI) - sometimes laggy UI transitions, typing really quick with SwiftKey keyboard is impossible, it's like the phone can't keep up with what I'm clicking fast, feels majorly laggy.

Anything I'm missing? and low performance/battery saving settings I'm missing? what's happening... oO

What's the difference between the H815 and the H815L

Hello, I'm the owner of the H815L (official Israely version) variant for about a month. The only differences that I have noticed between the H815 and the H815L are the bootloader and some minor change in the LTE network (for the IL network). But basically I infer that they are the same in hardware and software (expt the things bellow). So my question is to know the differences between those two variants because I would like to install TWRP on it and also CM 12.1 and maybe some custom kernel. So I thought that if there's not much difference between those two models maybe I could install on my device those versions for the H815 (because there won't be much support for this model).

Can you help me with this and tell me the differences and if could do the actions that available for the international version?
Thanks