Dear Arif,

If you have not yet designed/ordered your primers, please do as suggested above. If you have already purchased the primers, all is not lost. I have amplified genes using primers with greater than 10 degrees difference in calculated Tms. Do a gradient PCR to find out an annealing temperature that yields you desired amplicon. You can also try touch down PCR. But then again, it does not take long to redesign primers and order them. It will save you time and resources.

I've been told the rule is to keep the difference in Tm to 5C or less. 

Should I prepare new primer

Indeed, designing new primers is a good idea. If you haven't had the chance, NEB has some guidance on PCR at the following URL

https://www.neb.com/tools-and-resources/usage-guidelines/guidelines-for-pcr-optimization-with-thermophilic-dna-polymerases

you should design new primers at similar annealing temperatures. For pcr to work you have to use a temperature based on the lower annealinh primer. This means that the higher annealing primer can anneal all over the genome as shorter fragments of its sequence can anneal independentlyso the amplification will be messy

Dear Arif,

If you have not yet designed/ordered your primers, please do as suggested above. If you have already purchased the primers, all is not lost. I have amplified genes using primers with greater than 10 degrees difference in calculated Tms. Do a gradient PCR to find out an annealing temperature that yields you desired amplicon. You can also try touch down PCR. But then again, it does not take long to redesign primers and order them. It will save you time and resources.

 All what have been said is great even though I have used FWD/REV primers with more than 10C difference in Tm and they worked. Some times in those cases you need to set the PCR Tm a little bit below the lower primer Tm you use. Sometimes you amplify some non-target bands in such cases.

Good luck