There's various tradeoffs you can make when dealing with thermocouples. In reading EGT (exhaust gas temperatures) you're only worried about temperatures >500c up to your 1500C. Also, it depends on what accuracy you require. At a pinch, I would suggest you use an op-amp rather than the AD597 and offset it so your area of interest falls within 0-5v. For a 10bit adc, 500-1500 would equate to approx 1C per count. You can choose to ignore cold junction compensation if you're not worried about a few degrees of error or just use a semiconductor temp sensor and compensate in the software.

Otherwise you could use a 12bit adc and just scale the 0-15 to 0-5v(or whatever the adc input range is).