How long can it take for a new flight to fill up?

Just started a new airline in Iran, I am flying a Superjet from Terhan to antalya thinking it would be a good initial "international" flight, after 3-4 days barely getting 5 passengers either way on these flights?

I think you need to have more connections to feed that flight. Also each route has different demands. The route you chose might had a low demand

Can you check the demand for a flight on market analysis page?

No

No

Thanks! 

You have to try.

A look at real world flights help to find routes with demand.

I shall do, looking up busiest routes in iran at the moment, not much on it really! 

Also, do some research on the other servers might also help you. You will have some idea about which market might be good to fly to. But you just start your airline, try to serve all the airports in Iran first, then go international.

Cheers for the advice, after 2-3 days loads inter-iran are mostly 100% so far

so add more flights :)