Yes. Your ramp package needs much improvement. Your entire mana base could use some work.
First off ...
Chromatic Sphere,
Chromatic Star, and
Expedition Map are NOT ramp. They fix your mana ONCE. But mainly they draw you a card. They do not put you ahead on mana. Dump them.
For a 5 color deck, I recommend skewing your mana base toward one color. The color you want to play your early spells. Usually green.
For ramp, focus on cheap green spells, like
Birds of Paradise,
Rampant Growth,
Kodama's Reach,
Cultivate.
And then mana rocks that make mana of any color. Like
Arcane Signet,
Fellwar Stone,
Darksteel Ingot,
Cultivator's Caravan,
Commander's Sphere, etc (there are plenty to choose from). (Solr Ring is still a great ramp choice.)
You probably want at 10 to 12 ramp spells between your rocks/dorks/spells.
For your lands, only use lands that are capable of making green. This includes lands that make mana of any color -
Exotic Orchard,
City of Brass,
Grand Coliseum, etc. The ones that don't enter tapped are best, but with a 5 color deck, if you have to use a few that enter tapped then do so. For the duals, only use those that make green. Cut all those that can't make green. A few fetches would be good too. If you have the "pay 1 life" fetches, then great. But
Terramorphic Expanse and
Evolving Wilds work fine too. Be sure to include 2 or 3 of each basic, as fetching a basic will be your best form of color fixing.
Sisay isn't a cast-as-soon-as-possible commander. You want to wait until you have 8 mana available. By focusing on green mana and mana of any color, then by the time you have 8 mana, you will be able to cast Sisay and activate her.