Landlord wants to increase rent by 15% — what are my options?

Been in my flat in Manchester for 2 years. Landlord just sent a Section 13 notice proposing a 15% rent increase from £950 to £1,090 pcm.

I know the market has gone up but 15% feels excessive. The flat also has a few maintenance issues they've been slow to fix (broken extractor fan, damp patch in the bathroom).

What are my realistic options here? Can I challenge this?