(Updates with economy in paragraph 2, background in paragraph 3, quote in paragraph 4, net interest income in paragraph 5, graphic)

FRANKFURT, Feb 15 (Reuters) - Germany's Commerzbank on Thursday posted its biggest profit in 15 years in 2023, a 55% increase from the previous year, as it benefited from higher interest rates, and the lender said it was aiming for another profit rise in 2024.

But the bank warned that the sluggish economy "will remain a challenge".

Full-year net profit was 2.224 billion euros ($2.39 billion), up from 1.435 billion euros a year earlier and ahead of expectations for 2.191 billion euros.

Commerzbank, one of Germany's best known banks and partially held by the government after a bailout more than a decade ago, spent much of the past three years in a major overhaul, slashing its workforce and branch network to restore profits.

"We will achieve a further increase in net profit for the current year," Chief Executive Officer Manfred Knof said.

Like many banks, Commerzbank is benefiting from a rise in interest rates and the income that generates. Net interest income rose 8.5% in the fourth quarter to 2.126 billion euros, better than expectations for 2.081 billion euros.

For the fourth-quarter, net profit fell 16% but it was better than analysts had expected.

Net profit of 395 million euros in the quarter compared with a profit of 472 million euros a year earlier. Analysts had on average expected profit of 361 million euros, according to a consensus forecast published by Commerzbank. ($1 = 0.9321 euros)

(Reporting by Tom Sims and Matthias; Editing by Kirsti Knolle, Muralikumar Anantharaman and Kim Coghill)