TDA1085 power supply question
From the datasheet one might conclude that R10 is tuned by measuring. 
(On page 3 you have the section for VOLTAGE REGULATOR which can give additional clues)

And R15 is involved in a calculation with the C14 capacitor to determine que frequency (albeit the formula is not given).
On page 3 you have the specification for pulse duration in the TRIGGER PULSE GENERATOR SECTION: Trigger Pulse Duration (CPin14 = 47 nF, RPin15 = 270 k)

You can also start with the values used in some existing circuit like  (which has also 47nF for C14):

Beware the given schematic is for 230V.