If you put a 48 straight edge up against the most sunken areas there s a gap of almost a 1 2.
Tiling very uneven walls.
Preparing an uneven wall surface plastering.
One very big problem that not many people realise if the wall isn t really flat a brick joint pattern will show off every out of plane point in the wall by virtue of sticking out a half tile from the tiles above and below it.
If you don t think you can trowel a coat of mortar to get it even withing about 1 4 the tiles will further even it out when set i would investigate a possibility of mounting a cement board onto the bricks instead.
The problem is that the wall is uneven.
The board will create a perfect backing that will make setting tiles on thinset look like a walk in a park.
This is known as lippage and it can diminish the most professional of.
The mortar is spread.
There is also a spot near the window trim where the wall appears to be built up too much enough so that the tile could end up proud of the trim which i m pretty sure won t look so hot.
If you re tiling over an uneven section of wall the corners of the tiles may stick out slightly from the rest of the tiles.
Plastering a wall can be a super straight forward task but if you have no prior plastering experience it may be worthwhile getting a professional in to help achieving a perfectly flat surface for tiling is essential and this isn t always easy on your first attempt.