Uk transit visa

[Olia]

Hello guys, I really need your help.

I am an owner of Ukrainian passport, holding US B2 tourist visa and a Schengen visa, going to travel: Berlin - London - Chicago (3 weeks) - London - Berlin.

There are 3 hours wait time in London heathrow (I am not going to leave the airport) so basically my question is : Should I have any UK transit visa? I've found some info on government web site (links are below) but would really appreciate if somebody could give me an additional advice.

https://www.gov.uk/government/publications/changes-to-transit-visas-immigration-act-2014/changes-to-transit-visas#direct-airside-transit-visas

https://www.gov.uk/check-uk-visa

Thanks a lot!