When i ran sub 15 min, i was running quite much.
Around 30 - 60 miles a week off running
200 - 325 miles on the bike
And 15 - 25 miles off swimming
Depending upon where we where during the season.
You should increase your running too a level, that you feel you can put in the necessary mileage. With out skipping mileage and time spend, swimming and cycling.
this is an example week during the winter
Mon: 10k ( 7:00 )
Tues: 3*500 4*400 5*300 6*200
( 1:26 - 68 - 48 - 32 )With 3 min serie rest and 60 sec between intervals.
Wens: 8*1000 ( 2:52 ) 500 m jog in 2:30
Thurs: rest
Fri: 6 miles ( 5:30 ) + 8*200 ( 30 ) 60 sec rest
Sat: 10 miles Alterning pace ( 6:30 - 5:15 )
Sun: 15 miles 6M ( 6:30 ) 4M ( 6:00 ) 3M ( 5:30 )+ cooldown and warming up off 1 Mile