I have the Rawkins book on the Hanoverian army 1813-1816, worthy addition if you can find it. There's too much info to type out here
Feldbataillon Langrehr has two uniforms depending on date:
March 1813 as Batataillon von Rohl: 8 companies, black knee length litewka frock coat with double row of 6 white metal buttons, light blue collar, black cuffs with no piping, light blue shoulder straps. Prussian shako with black waxed cover. Black pants
In June 1814 the battalion became Nr.3 Feldbatailln Hoya, with new uniforms - British stovepipe shakos with brass oval plate, white shako chords, back cockade, short white plume. By August 1814 some had Briitsh red coats with light blue facings, grey pants. Black cross belts throughout.
There was a "sharpshooter section" within the battalion, distinction details not confirmed.
The Lauenburg Regiment is more difficult, as no primary source or uniform has survived. It says the Nafziger reference is confused with Btn von Rohl
In April 1813 it has British plain stovepipe shakos, already has feldmutze with madder red or dark blue soft crown and headband. 25% of the unit was still wearing these in 1815. It had British coats with cornflower blue facings. White cotton trousers in early 1813, replaced by grey wool trousers from August 1813.
White cross belts, French style brown backpacks and breadbags.
So, in 15mm for 1814, the visual ques might be:
Langrehr: British style uniform with stovepipes, light blue facings, black cross straps, no backpack or British style backpack?, black pants
Lauenburg: British style uniform with a mix of plain stovepipes and Prussian feldmutz caps, cornflower blue facings (so slightly darker), white pants, brown French style backpack.
The only wings mentioned for the Langrehr are a possibility in the sharpshooter section, otherwise light blue shoulder straps edged in white, with a white wool 'tuft' at the outer tip.
In reality it does depend on which year, and which part of the year you are fielding.