Hi,
There are a couple of options, it depends on the substrate!
New houses are generally plasterboard walls / partitions and therefore it is easier, cleaner and cheaper to remove tiles with the plasterboard, all you do then is fix new plasterboard and you have a perfect new surface for tile on, depending area I use tile board for showers etc.
Or, if the original tiles were easily removed and left the old tile adhesive you can carefully apply a steamer to the area, this sometimes softens and will aid the removal, a messy option and can compromise the plasterboard.
If you don't want to comb the adhesive on the wall then it will be fine to leave the old adhesive and coat the wall with a PVA sealer, leave to dry and use the old dot and dab method for reapplying the new tiles. This method can be more time consuming but will produce a satisfactory result.
Just read the additional text, if you are tiling the whole wall I would scrape it off, again here you could just steam it, if it was me I would probably re-plaster the wall and then tile it.
It comes back too, “How much work you want to put it, How good of a job to you want at the end”
Personally, sanding it would be a very messy and big job unless you have a powerful belt sander.
Hope this helps.
