I see... That's quite hard to make such exact estimate based on those. When we look at wikipedia
article which is also using Maddison, we will see for 1880 that actual Spain has 28k and Ottomans have 18k which is after loss of Bulgaria, Bosnia, parts of Serbia and Greece, as well as Kars and Cyprus (together with those countries would be closer to 25, almost equal), and years of war, bankruptcy, rebellions and crysis. I would argue that Spain's advantage isn't as big as 55%, but these sources convince me that indeed should be at least a little bigger.
Fair, I probably should have said 35-60% or similar. I'm sometimes not great at emphasising uncertainty even when I intend to.
Though, remember that Spain too had undergone plenty of costly wars (the 3 Carlist Wars, Cantonal Rebellion, highly expensive colonial wars such as the Ten Years' War, and over
a dozen attempted coup d'etats, several of which successful) and decades of general stagnation (if not nearly as severe as for the Ottomans), and that the Ottomans had regained the Levant (Syria, Lebanon, Jordan, Palestine) and Hejaz (and Egypt, but Egypt is for some reason listed under the British Empire in the article you linked, despite not being invaded by the British until 1882) in 1880 which would mostly make up for the parts they'd lost in the Balkans they'd lost by 1880 (they still held most of Greece) compared to 1836. Just looking at population, the population of the Levant, Hejaz and other territories gained was combined roughly 4 million in 1880, whilst the population of the territories lost between 1836 and 1880 in the Balkans was at most 4.5 million, probably significantly less (and the GDP per capita was roughly the same in the Levant as in the Balkans, in some places even higher. For example, Syria=1403, compared to Bulgaria=1339. Only part of the Balkans significantly richer than the southern Ottoman Wilayats was Greece at around 2000, but the border changes between 1836 and 1880 in Greece were fairly insignificant with at most a couple hundred thousand inhabitants).
The relative difference between the Spanish and Ottoman GDP in 1880 was probably not really
that different than in 1836 (even if the state was in a worse situation in general).