Your EU SIM will incur standard international roaming charges here. Consider a local SIM or eSIM.
Roaming Zone Memberships
The East African Community implemented the One Network Area (ONA) framework starting in 2014, which limits roaming surcharges between member states to a maximum of US$0.10 per minute. The EAC aims to eventually eliminate all roaming charges entirely. Member states include Kenya, Uganda, Tanzania, Rwanda, Burundi, South Sudan, DR Congo and Somalia.