Total War Attila - Occupy city with other religion

Hello, How do I handle converting cities/buildings while occupying other settlements with a different religion?

As en example, I start as Ebdanians, I attacked the West roman city Segontium (and Razed it) and there is almost no Celtic paganism in this area so to colonise it is extremely expensive, like 9k while you earn maybe 1,3k per turn.

Also if you occupy it and then want to convert the city it is the same, like 8 rounds to convert it and it cost 8-10k just because the religion is so low.

Also it take some time to get the religious building up but even if you have them and have a priest it takes enourmous amount of time for the priest just to stand in the area for the religion to go up so that the converting is cheaper.

I just end up clicking next turn because I dont have the money to colonise (for the razed cities) or dont have the money to convert the building when I have occupied the city.