Anyway, back to the subject matter. Using the Tulse Hill Bridge as an example, the proposal there is (or at least was) not to raise the height of bridge, but to replace the metal deck and support columns with a ****ing great concrete single span deck. Then, if an errant lorry or bus does hit the bridge, a) the vehicle will come off rather worse, and b) the bridge will stay precisely where it was, and there would be no need to stop trains pending inspection.
The same could probably apply at Mortlake Rd in Kew, although that deck looks much newer.
One of the problems with Tulse Hill (Thurlow Park Road) is that the obvious option of lowering to achieve the height isn't really available as you can't lower the road as that would damage the support column foundations (some work was done around 1990 ish that saw a concrete raft put under the road surface under the bridge and surrounding area). If the deck is replaced, the support columns go and the road can then be lowered to achieve greater height clearance. 15'6" should be relatively easy to achieve but 16'6" should be do-able depending on the bridge deck and how much TfL would want to spend.
Catford (15'9") has similar support column issues to Tulse Hill so a new deck and then lower road would be needed too.