Ubuntu/Xubuntu works much slower than Windows 10

I've installed Windows 10 and Ubuntu 16.04 (also tried Xubuntu 16.04/14.04) on my brand new laptop i5 6200u/8gb/gt940m/240gb. I have problem with ubuntu performance, which doesn't occur on windows, where everything i've tried works just fine. On ubuntu I feel lagging when just typing - e. g. in codeblocks or in chromium.

In gtkperf i receive very different results - once it's like 2,5s and next time 20-30s (!).

I tried reinstalling ubuntu couple of times, with swap and without it. Also on empty ssd - with no effect at all. Memtest - no errors, ssd benchmarks - fine, cpu benchmarks - common results (benchmarking under windows).

I wonder if someone can tell me what causes my problems - thanks in advance!