Is the risk of alzheimer's greater for someone with an aneurism 15 years ago?

No: The exact "cause" of alzheimer's dementia is unknown. Excess beta-amyloid protein and excess aluminum in, say, dialysate solution (for those on dialysis for renal failure) have been implicated. Vascular dementia is much more common: this is simply atherosclerosis of the brain's vasculature, aka hardening of the arteries. Avoiding tobacco and exercising are your best defenses against dementia.

Glad you survived.: No, the intracranial bleeding does not cause alzheimer's, but may be associated with another cognitive impairing entity, normal pressure hydrocephalus, which would be diagnosed only if you develop a gait apraxia, urinary incontinence, and memory loss. Really, do not worry, as it is infrequent. Enjoy life, you made it! (you see, about 50% of aneurysmal ruptures die before reaching hospital).