Caution, the transformer nameplate rating must be rated for that. Yes, a 115deg rise transformer does have the overload capability because the insulation rating imost likely is 220degC. The normal 150degC rise transformer is based upon a 40degC ambient+a 30degC winding hot spot allowance + 150degC rise= 220degC. With a 115degC rise design you have a 35degC margin which is basically intended to extend transformer life because of the lower temp rise.
Also note that the internal conductor and terminations are based upon the transformer's nameplate rating and unless the transformer is designed for the extra load such as an FFA (future fan to air) rating on the nameplate it isn't rated for fans nor should a 115degC rise transformer by applied as though it were 150degC rise.
What is included in the nameplate on the transformer is the key.
But for temporary overloads a 115degC and 80degC transformer have a 15% and 30% overload capacity respecively without exceeding the insulation class of 220degC.
It must be noted that ambient temperatures is also an important consideration.