I should be clear that personally I would support 15 minute clock face schedule, but I do think I should point the arguments people are going to make against it.
When comes to people at the station just asking for place they tend to just want the train to be where they're going to be not that long of wait, but when they're considering it for the inevitable consultation the time factor always creeps in.
Another issue is probably going to be the freight from Trafford Park which always takes a long time to get on or off the mainline.
For reference on the rare occasions it runs the Northern express takes about 17 minutes Oxford to Warrington.
Anecdotally I would generally take main stations as the one's I'm asked for which is usually; Warrington Central, Liverpool South Parkway, Birchwood, Warrington West, Widnes, Irlam, Urmston and Hough Green.
If I had free reign and assuming the line were to remain heavy rail, electrified and made an every 15 minute suburban service I would aim to keep Warrington Central at no more than 30 minutes to remain comparative with the driving time. I would consolidate and remove stations as necessary between Manchester and Warrington; Trafford Park and Humphrey Park closed and new station created between Park Road and Barton Road to replace them, Chassen Road closed with more bus feeder routes concentrated on Urmston and a much larger park and ride facility at Flixton and, Glazebrook and Irlam new large park and ride west of Moss road near to current loop location with new access road via the old rail alignment from the south east.