I dropped a PM to the OP, but in case other FTers may require similar info:

1.5 hours is too tight at KBP regardless whether or not one is traveling on a through ticket. Domestic flights are operated from a different terminal. Pax have to collect their bags and check them in at the international terminal. Even though Dnieproavia has good on-time record regional airports in Ukraine are very susceptible to weather delays during winter times. There is immigration control when departing KBP but the lines are never very long. In short, 90 minutes is doable but everything needs to be on time and a lot of running/worrying will be involved.

P.S. Andriyko is a he.