The fuel designation number represents the octane number. Aviation fuels run on an octane range, with the first number being the lean mixture anti-detonation or octane figure, and the second being the top of the rich range. You can think of it as anti-detonation protection throughout the engine operating range...in this case 115 being your idle protection, and 145 being your rich, full power protection for high power settings.
100 octane aviation fuel was a shortened version of 100/130 (green), with an octane range for lower power, or smaller displacement engines. Since that time, we have 100LL, which desipite the name "100 low lead" is actually quite high in lead content...tetraethyl lead being one of the primary tools used to control detonation and establish a specified detonation resistance in aviation fuels.
Use of fuels designed for bigger engines...and 115/145 is for bigger radial engines...may lead to higher incidences of spark plug fouling, especially if you're using massive electrode spark plugs. Continental recommends post-flight engine runs of a minute to a minute and a half, between 800 and 1000 rpm, to normalize the engine and clear deposits. When this is done, you should go to idle cutoff with the mixture from this RPM range and power setting, rather than retarding the power to idle first...run it for a minute and a half in the parking spot at 1000 rpm, and pull the mixture to cutoff from there without touching the throttle.
All Continental motors that were certified on 100LL or 100/130 will run fine on 115/145, but will still foul more easily and are susceptible to combustion chamber deposits as a result of the higher tetraethyl lead content. It's also recommended that you reduce your oil change intervals. I always recommend a maximum of 50 hours between oil changes, with 25 under unusual operating conditions (dust, etc). Many aren't aware that increased lead buildup in oil occurs which can have an effect on engine operation, such as sticking valves. This is most common in engines not designed for hig lead fuels, such as smaller piston powerplants that ran on 80 octane. Lead buildup in the oil contributes to deposites on valve stems and can cause valve sticking and increased valve guide wear.
When you're buying fuels in the East, take care to sample it very carefully. Globally aviation fuel tends to be fairly uniform in content and specification, but in the East you may find some variation in the quality and content. Without sending the fuel to a lab, you won't know for sure, but you can check for the obvious contaminants like water and debris. Remember to allow your fuel to settle out for a half hour after filling the tank, to allow contaminants to be available at the fuel drains for sampling.
Read over this paper for some highlights on the topic:
www.fsv2000.at/woche/2001_10/conti_sb_m77_3.pdf