If one is next to a sefard minyan that does Birkas Kohanim should he or could he go listen even if he will miss a kadish or kedusha of uva letziyon?
There is no obligation to answer kaddish etc. to other minyanim while you are davening, if you want you may. However if it is going to hinder your davening, i.e. you will miss kedusha, etc. or even it merely hinders your concentration, you shouldn’t answer to it.
Halichos Shlomo (Tefilla) 6-12, ftnt. 42-43. Orach Neeman 109-12.