This is probably a Prussian regiment you have never seem before because it was composed of captured Saxons, many of whom took the first opportunity to desert.
In 1756 the Saxon army surrendered to the Prussians at Pirna. Frederick forcefully created 10 new regiments from these chaps plus a further 5 converged grenadier battalions. Most deserted within months although this regiment IR55 seems to have lasted longer than the others. It would probably have been better to have mixed the men in with existing regiments rather than creating new ones and Frederick's poor judgement was repaid with mass desertion.
More details are available on Kronoskaf. Figures are mostly from Foundry (standard bearers are from Crusader) and it is rather nice to return to them as they are simpler than those from Black Hussar.