The service between T1&3 and T4 always was every 15 minutes, or at least it was supposed to be - whilst T4 was served by the half-hourly Heathrow Connect train, what happened was that it also provided a shuttle service to T123 in between departures back to Paddington - perhaps it's easiest to explain it by showing the movements of each Heathrow Connect train:

Paddington -> Ealing Broadway and other intermediate stations -> T1(2)3 -> T4 -> T1(2)3 -> T4 -> T1(2)3 -> Ealing Broadway and other intermediate stations -> Paddington

The potential problem came when the Heathrow Connect train was running late arriving from Paddington, in which case the shuttle between T4 and T1(2)3 would get cancelled to ensure that the train was on time heading back to Paddington. The new arrangement of there being a standalone, dedicated (Heathrow Express branded) shuttle train means that service disruption elsewhere no longer affects the shuttle service between T1(2)3 and T4 any more.

I reckon the OP should take the Tube and meets his friend at the T4 Tube station, as WHBM suggests above, but otherwise he should take the Heathrow Express shuttle - the bus is the long way around.