Hyh:
Can anyone state how likely a fine would be from DVSA for going 1.5 hours over and how much the fine would be ?
According to an old FTA Guide
Regular daily rest – less than 11hrs(no reductions left)
Less than 11hrs but more than 10hrs rest £60
10hrs or less but more than 9hrs rest £120
9hrs or less rest £200
These have gone up since then to, I believe, £100, £200 and £300 respectivaly so the OP’s offence would be £200.
They can also now go back 28 days at the roadside, so keep it clean, put it down to experience, and unless you work for a dodgy bunch and get a DVSA visit to the office it will be done in a month.
Hyh:
Also OP, I’m assuming you don’t work for one of the big boys like DHL etc. In which case, are you more likely to be pulled on a random check? If so, a new tachocard for £17 might be worthy insurance, unless the previous card’s data will be transferred to it the next time you download it at the yard?
I believe that might be considered fraud, 
so unless you plan to be a serial offender, its probably better if stopped in the next month just to put your hands up and if you can’t talk your way out if it pay the fine. Join URTU and you might benefit from their hardship fund.