Bkk connection - question

Hi, I need help with a transit question at Bangkok (BKK)

We have the following flight:

05/06 - SV844 Jeddah to Bangkok with Saudia, arriving at 13:40.

And we bought a ticket to Hong Kong with Hong Kong Express (UO701) for the same day. The issue is the flight was modified and now leaves at 16:15 from BKK. Does anyone know if we need to go through immigration? We are not checking any baggage.

Thanks!