Welcome to the forum, Wingfinger
I've always found that treadmill running is different to running outside, don't really know whether one's harder than the other.
As for speed / distance, I suggest you just keep at it for a while. Once your body gets a bit more used to it, you will likely increase both fairly rapidly, especially since your basic, core fitness will be decent from doing weights and swimming. 1 1/2 miles in 14 mins is about 9? mins per mile; not too challenging. How fast you can go for how long really depends on you yourself though, everyone's different.
My suggestion - Just keep doing regular runs maybe 3-4 times a week for a couple of months, and see how you go. Perhaps you might like to try one of the numerous fitness programmes you can download. If after two months of decent effort, you're not yet at your target, give it another month and really concentrate on upping your distance and / or pace each week.
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