1742
Having sustained a severe loss in killed and wounded at Carthagena, and also from the effects of climate, the regiment returned to England in 1742, and commenced recruiting its numbers.
1743
1744
During the years 1743 and 1744, the regiment was stationed in Great Britain.
1745
In the meantime, a British army was supporting the interest of the house of Austria on the Continent; but the French monarch brought so great a superiority of numbers into the field, that the allied army, under His Royal Highness the Duke of Cumberland, was unable to prevent the enemy gaining possession of several fortified towns in the Austrian Netherlands, during the summer of 1745. Under these circumstances the regiment was sent from England to Ostend, with the view of contributing to the preservation of that place, where it arrived on the 27th of July. The French besieged Ostend, which was defended by a garrison of British and Austrian troops under Lieut.-General Count Chanclos, of the Austrian service, who capitulated after a siege of thirteen days, the garrison being permitted to march out with the honors of war, and proceed to the Austrian territories. The Fifteenth joined the army.
At this period, Charles Edward, eldest son of the Pretender, had aroused the Highland clans to arms, and asserted his father's pretensions to the British throne. This rebellion occasioned the regiment to be recalled from Flanders: it arrived in the river Thames, and landed at Gravesend, on the 25th of October; but it was not ordered to march against the insurgent clans—it was destined to remain in the south of England, to oppose the threatened invasion of the French.
1746
When the hopes of the Pretender had been annihilated by the battle of Culloden, on the 16th of April, 1746, part of the military force of the kingdom became disposable for other services, and the Fifteenth regiment was selected to form part of an expedition against the French possessions in Canada. Various circumstances occasioned the fleet to be detained so long, that this enterprise was deferred, and an attempt on the port of L'Orient, the principal station for the French East India Company's shipping and stores, was resolved upon. The expedition sailed from Plymouth on the 14th of September; on the 20th a landing was effected on the coast of France, and the troops assembled to oppose the debarkation were driven from the shore. On the following day, the British advanced in two columns towards L'Orient; the Fifteenth forming part of the second column. The French militia fired upon the troops from the woods, and put the men of one or two corps into some confusion, when Captain Honorable James Murray led the grenadier company of the Fifteenth forward with great gallantry, and dispersed the enemy. When the leading companies arrived at the village of Plemur, they were fired upon from the houses; but this resistance was speedily overcome, and the people were punished for their temerity. On arriving before L'Orient, the governor proposed to surrender; but the conditions demanded were not acceded to, in consequence of a report of the engineers stating the practicability of reducing the town. The siege was immediately commenced; but the artillery and stores with the expedition proved unequal to the undertaking, and the troops retreated to the coast, and re-embarked without molestation.