Experience of riders switching from 170mm to 150mm cranks is no change in ratios is required. Gears used are same as before. A 5mm change is unlikely to do much at all.
BFC above has it correct. I would have said 'useful' or 'comfortable' rather than 'safe', but that's me. If you can pedal the bike you will be fine. Pedaling mechanics, which is you, is way more important than fine details of bike mechanics.