The other thing is did you tank it - or not?
This is a bog-
standard shower cubical with tiles stuck onto plasterboard and plywood.
Is that similar to what you have done?
Our tiler realised it at the stage above so he STOPPED.
He took the tiles off and then he waterproofed the cubical by using a tanking kit (see tub above) and then he painted all the surfaces with the waterproofing paint, plus we reinforced the corners with mesh.
Once dried the cubical was tiled.
I'm going to assume that you did nothing and that you just spread adhesive over plasterboard and then grouted. And I will assume your shower looks similar to the piccie above....
If that's true then your weakest point will fail over time. Might be a joint, tile edge, shower edge, control value. But anywhere where water can get in will start to weaken the plasterboard. As mentioned above you might be lucky and it will takes years, or it might take months.
The plasterboard will soak up water and then slowly expand. You might find tile sections popping off. If that does happen sometime in the future then its re-tile from scratch but then just use the better materials.