Depends on whether you are on grass or tarmac. Strong winds for taxiing on grass can be a pain if you are trying to turn on wet grass or muddy conditions. 15 kts can be awkward in these conditions. Tarmac obviously is better therefore. Other than that i think quite strong winds, 25 - 30 kts are ok for taxiing, just that maybe you ought not to get airborne as it will be more "sporting" upstairs!
When isend a student solo the flying conditions usually take over the taxiing conditions, so is not normally a factor. If he / she will find it difficult to taxi, then he will find it difficult to take off and land too.
172 has a bigger keel area than a 152 and so is affected more.
KK