I Googled and found these 9 Sunni mosques in Tehran,
1 - Sadeghiyeh mosque, located at the Sadeghiyeh second circle,
2 - Tehran-Pars mosque, located on Delavaran street,
3 - Al-Quds mosque, located at 20km on the old road,
4 - Persian-Gulf mosque, located in Fath,
5 - Al-Nabi mosque, located in Shahrak Danesh,
6 - Haft-Choob mosque, located in Mallard road,
7 - Vahidiye mosque, located in Shahriar,
8 - Nasim-e-Shahr mosque, located in Akbarabad,
9 - Razy-Abad mosque, located in Shahriar forked-road.
Since I am not so much into religion I can't give much information about Sunnis in Iran but I think there shouldn't be a major problem for most branches of Sunnis in Iran (Considering the fact that 9% of population of Iran itself are Sunnis which equals to almost 7M). However I do believe they are not really good with Wahhabis.
Hope I am right and could help.