Bit of main loop code to give you a some ideas.
time=millis();
if (time >= loop2){
loop2 = loop2 + 15;
//do your 15ms stuff here
};
if (time >= loop3){
loop3 = loop3 + 750;
//do your 750ms stuff here
// I do read scratchpad of DS1820 followed by next call to update scratchpad with temperature at this point
};