Hello, can someone please help me..............

Equation dT/dt= -k(T-8) where T is temp degree celsius.... what is the upper and lower limit of k for the temperature to remain constant at 15 between t=0 and t=8???????................ Does a reduction in the rate of heat loss correspond to an increse or decrease in k?? What does this say about the insulating properties of k??????

Thank you for your time... i really appreciate it!!!!!!!