A LM7815 has a quiescent current of about 5mA, so that's 130mW dissipation just sitting there with a 26V input, + load dependent dissipation of its input to output voltage drop times its load current. At 50mA load current the total dissipation would be 680mW.
Similar figures apply to the 7915 negative regulator.
N.B. You *MUST* use the recommended decoupling caps (see datasheet) on the input and output of LM78xx and 79xx regulators and connect them as close as possible to the regulator. Omit the decoupling and if you are unlucky they can act as a RF power oscillator, 'singing' like a canary at a few tens of MHz. Unless you scope their output with a 50MHz or better scope, the only clue you'll get that they are misbehaving that way (apart from the missing or badly located decoupling) is that the output voltage is significantly out of spec, and its load will most likely be malfunctioning extremely weirdly.
Caution: Unlike the LM78xx series positive regulators, the heatsink tab of a LM79xx negative regulator is connected to its inout pin, not to ground. If you bolt one down to chassis or a grounded heatsink, you must use a silpad or other electrically insulating thermally conductive heatsink washer under it and a top-hat insulating washer on the screw.